This invention relates generally to machining processes, and more specifically, for example, to methods for fabricating turbine engine components.
At least some known gas turbine engines include a fan assembly, a compressor, and/or turbines that include a rotor disk having a plurality of rotor blades, or airfoils, that extend radially outward therefrom. For example, at least some known rotor blades are coupled to the disk by a dovetail that is received within a corresponding dovetail slot formed in a supporting perimeter of the rotor disk. To facilitate enhanced performance, at least some engine manufacturers have attempted to increase the number of blades within each rotor assembly. However, as the number of rotor blades increases, the disk perimeter may not have sufficient material to support the increased number of blades within acceptable stress limits. Accordingly, at least some known fans, compressors, and/or turbines are fabricated with a rotor “blisk” wherein the rotor blades are formed integrally with the rotor disk in a one-piece assembly. The unitary assembly may reduce the centrifugal stresses induced to the rotor disk.
However, the manufacture of a rotor blisk may be more complex than the manufacture of individual rotor blades and discrete rotor disks. Moreover, because the rotor disk and rotor blades of the blisk are integrally formed, manufacturing defects may be more critical than those associated with individual rotor blades and discrete rotor disks. For example, if one or more of the rotor blades within a blisk is outside acceptable manufacturing tolerances, the entire blisk may be deemed defective and unusable. Accordingly, the manufacture of a blisk may require more diligence and/or compliance with manufacturing tolerances than the manufacture of individual rotor blades and/or discrete rotor disks. Accordingly, such enhanced compliance and/or diligence may increase time and costs associated with manufacturing an engine as compared to other engine assemblies.
At least one known method of manufacturing a blisk includes machining the blisk from a blank using a rotating mill and a step milling process. For example, using a bottom of the rotating mill, one or more grooves are rough-cut across the blank to partially create two opposite sidewalls that will eventually each form a side of adjacent finished rotor blades of the blisk. Portions of the sidewalls are then finish-cut using a side of the rotating mill. Each groove rough-cut and sidewall finished cuts are then alternately repeated to machine deeper into the blank to form a pocket within the blisk. By rough cutting the pocket depth in increments and alternatively finishing the sidewalls in turn, the step milling process forms a pocket having a convex side of one of the adjacent rotor blades and a concave side of the other adjacent rotor blade, both finished within accepted tolerances. The blank is then indexed and the step milling process is repeated to form the next pocket and finished sides along the perimeter of the blank.
To facilitate preventing excess wear of the mill, a different but generally similarly configured rotating mill is sometimes used to form different pockets of the blisk to avoid excess wear of each mill. However, forging stock material may need to by removed from portions of the finished rotor blades, such as leading and/or trailing edge portions, which may increase a cycle time, difficulty, and/or cost of fabricating the blisk. For example, removing the forging stock material may necessitate more steps, operators to perform the extra steps, tooling, and/or operator training to fabricate the finished rotor blades. Moreover, because opposite sides of each rotor blade are machined using different mills, manufacturing variances may occur between the opposite sides. Furthermore, because opposite sides of the same blade may be machined at different times, a change in thermal conditions may cause manufacturing variances between the opposite sides. Such manufacturing variances, for example variances in blade thickness, may affect a performance of the blades and/or a dynamic balance of the blisk.